Sciencemadness Discussion Board

Sulfur trioxide from pyrosulfate: catalyst?

Gui316 - 29-9-2011 at 13:12

I was just wondering if there is any compound other than sulfuric acid to act as a catalyst on the decomposition of pyrosulfate salts to sulfuric oxide by heat.

[Edited on 30-9-2011 by Gui316]

AndersHoveland - 29-9-2011 at 13:20

Hopefully this will get you started:

CuO, ZnO, NiO

"thermal decomposition of alkali metal pyrosulfates into the sulfates, and a mecha- nism was proposed for this catalytic decomposition"
"At higher temperatures, α-Al2O3 acts as a promoter catalyst for the decomposition of pyrosulfate to sulfate"
"NiO reacts to some extent with alkali pyrosulfates forming the yellow NiSO4 and alkali sulfates as separate products. NiO and NiSO4 form eutectic mixtures with alkali sulfates melting at temperatures lower than those of the pure salts."

One of those papers seems a little amibiguous in its use of the term "pyrosulfate", as if it had gotten the name confused with "persulfate", so one should be a little hesitant to take all this information as truth.

Unfortunately, I do not think any of these catalysts are very effective at significantly reducing the decomposition temperature. Trying to get pyrosulfate to decompose is difficult, it requires intense heat, preferably with a steel/iron-bottomed distillation setup, since the molten sodium sulfate can be corrosive to glass at these high temperatures.

[Edited on 29-9-2011 by AndersHoveland]

Gui316 - 29-9-2011 at 13:38

Thank you very much! I'll be trying that later.

symboom - 3-10-2011 at 19:29

ive read some where where this reaction works producing SO3 then leading into water to make sulfuric acid
Sulfuric acid by pyrolysis of a mixture of sodium bisulfate/persulfate

[Edited on 4-10-2011 by symboom]

Gui316 - 4-10-2011 at 01:08

Leading sulfur trioxide to water indeed produce sulfuric acid. But that reaction should not be realized. Sulfur trioxide reacts explosively with water, making dense fumes of sulfuric acid and spliting highly acid solution everywhere. It must be reacted with concentrated sulfuric acid first, which is more safe and then diluting the acid in water, so you can get more sulfuric acid.

Endimion17 - 4-10-2011 at 01:44

It depends... A solid chunk od SO<sub>3</sub> will react by detonating, but aerosol won't react at all, or just extremely slow.

Magpie - 4-10-2011 at 07:52

I believe that the aerosol is SO3 that has already been dissolved in atmospheric moisture. If you ran pure SO3 gas directly into water I imagine you would get an explosion.

Gui316 - 4-10-2011 at 08:46

The fact is that it is not a very good idea to react sulfur trioxide with water directly if you don't have fancy equipament. And i don't intend just to pour (it will be a liquid here where i live) sulfur trioxide into a jar with water. I'm going to dissolve it in 98% sulfuric acid. Well, but to do that, I'll need to produce sulfur trioxide from pyrosulfate using a catalyst. It can be sulfuric acid, but it just don't sound very smart. Or I can use some oxides as pointed by AndersHoveland.

AndersHoveland - 10-10-2011 at 14:36

Something else that has already been discussed in this forum is the addition of boric oxide, which lowers the decomposition temperature.
Boric oxide can be prepared by driving out the water from boric acid, by heating.

(2)H3BO3 --> B2O3 (molten) + (3)H2O (steam)

The reaction is probably complicated, but could best be described as:
(2)Na2S2O7 + B2O3 --> Na4S2B2O11 (molten) + (2)SO3 (vaporized)
where the slag contains an borosulfate mass of indefinite composition

AndersHoveland - 24-1-2012 at 14:37

Here is the link to NiO being used as a catalyst in the decomposition of pyrosulfate to sulfate,
"Catalytic effects of copper(II) oxide and zinc(II) oxide on the thermal transitions of sodium and potassium persulfates"
M. M. Barbooti, F. Jasim, 2005, Iraq